Often referred to in the specifications as 'strong pull-up' this will drive the signal line high so that parasitic devices can obtain power from the bus.
This is normally followed by a delay and then resetting the bus.
Where OneWireBus is the name you have given to the device in Project Designer.
This will actually set the bus signal I/O pin high so that the current is being supplied by your micro controller pin. Since most one wire devices only require a small amount of current then this is satisfactory. However: if you are trying to code a new device that requires more current than the AVR is capable of providing (typically 30mA) then DON'T USE THIS METHOD as it will blow your AVR pin or worse.
Make sure you know what you are doing - if you use this call and a device then pulls the bus line low then you will create a short circuit and something will go bang!